I've seen this question pop up on many Facebook groups and forums. It's a great question, but unfortunately it doesn't have a super simple answer.
Here are a few things to consider when deciding if your pattern that calls for DK-weight yarn can be substituted with fingering-weight or 4 ply yarn
Not all DK-weight yarn is the same
When you look at the bands on various balls of wool you'll notice that the gauge (number of stitches per 10cm square will vary). DK-weight wool is sometimes referred to light worsted, or 8 ply yarn and it should have 21-24 stitches per 10cm. Some examples are:
- Double SUNDAY: 21 stitches per 10cm on 3.5mm needles
- Peer Gynt: 22 stitches per 10cm on 4mm needles
- Merinoull: 22 stitches per 10cm on 3.5mm needles
- Finull: 24 stitches per 10cm on 3.5mm needles
And to make matters trickier, Double Sunday can also knit up to 20 stitches per 10cm on 4mm needles, which could push it into being considered a worsted or aran-weight wool.
The same applies to fingering weight yarn
Fingering weight yarn can be referred to as 4 ply yarn, and it will fall between 27 and 32 stitches per 10cm - although the most common ones are 27-28.
Some examples are:
- Tynn Peer Gynt: 27 stitches per 10cm on 3mm needles
- SUNDAY: 28 stitches per 10cm on 3mm needles
- Lamull: 28 stitches per 10cm on 2.5mm needles
- Baby Garn: 30 stitches per 10cm on 2.5 mm needles
Your best bet is to knit a swatch
I know you were probably hoping to avoid this, but to get the best results you really should knit a swatch. Start using the needles recommended in the pattern for the DK-weight yarn (likely 3.5mm or 4mm) cast on twice the number of stitches that the gauge calls for (e.g. if the pattern gauge is 22, cast on 44) and knit approx 15cm in pattern. Cast off, give your swatch a quick bath, allow it to dry and then measure your gauge. If you have too many stitches per 10cm try a larger needle, if you have too few stitches per 10cm try a smaller needle.
Some tips for finding the right 4ply in your stash
I know you probably don't want to test every 4ply that you have in your stash, so here are some tips to try get close on the first attempt. Sandnes Garn deliberately made Double Sunday to be the correct gauge to make using two strands of Sunday to be equal to using one strand of Double Sunday. This gives us some hints of what to look for. If your pattern has a gauge of 21 using DK, then look for a fingering-weight yarn with the same specs as SUNDAY to replace it - 28 stitches per 10cm. If the pattern calls for 24 stitches per 10cm, then you will need to find a thinner yarn, with more stitches per 10cm - maybe try something with 30 stitches per 10cm as a starting point otherwise your project will end up too large.
One last point
Don't forget to check the meterage on your yarn.
For example, Double SUNDAY is 108m per 50g and SUNDAY is 235m per 50g.
If a pattern calls for 100g of Double Sunday, that's 2 x 108m = 216m of yarn.
If you replace that with SUNDAY, you'll have 2 strands held together so 100g/2 balls will give you 1 x 235m = 235m of yarn.
In this example, the fingering-weight yarn is longer than the DK-weight yarn, so you should have plenty for your project. In most cases this will be true - but it's always worth checking before committing to a particular yarn choice, especially if you're getting your yarn from your stash and it will be difficult to get an extra ball.